This invention relates in general to a control system for controlling a multi-phase motor with a plurality of electromagnetic field windings adapted to be separately energized in a variety of energization modes to control rotation of a rotor in the motor, and is more particularly concerned with such a control system including digital circuit means for generating a plurality of logic signals for controlling energization of respective motor field windings in either two-phase-on, one-phase-on, or one of a plurality of fractional phase-on modes with the desired energization phase mode selected by circuitry responsive to a feedback signal developed by detecting rotary movement of the rotor. The invention finds particular application in a high speed teleprinter of the type employing a multi-phase stepping motor for positioning a print head, wherein the stepping motor must be operated over a wide range of operating speeds with a high degree of precision and reliability.
In the operation and control of many motors, and particularly with stepping motors in which it is desired to control the rotational position of a rotor in the motor in a step-by-step manner, the motor windings are frequently energized in a sequential on/off manner from a D.C. voltage source. Such energization characteristics are particularly suited to and compatible with digital switching techniques. However, it is also common to develop an analog feedback or error signal by detecting the angular position and/or movement of the rotor in relation to energization of the field windings. Analog-to-digital conversion techniques to utilize the analog feedback signal to develop the digital winding energization signals are often impractical and uneconomical.
Furthermore, the duration of digital signals suitable for energizing the field windings must vary between wide limits to control the motor over a related range of operating conditions. For example, to obtain maximum motor torque during starting, acceleration or high load conditions, it may be desirable to simultaneously energize more than one field winding to develop greater rotor torque. During steady state operation of the motor at the desired speed and load conditions, suitable duration of field winding energization may be less than so-called "one-phase-on" wherein each field winding is sequentially energized and remains energized only until the next field winding is energized. During deceleration, reduced load or the like, the desired duration of field winding energization may be minimal or zero.
It is therefore a primary object of the present invention to provide digital circuitry for generating a plurality of logic signals adapted to control energization of respective field windings in a variety of energization modes such as two phase on, one phase on and in one of a plurality of fractional phase on modes.
A related object of the present invention is to provide phase on selection means responsive to a feedback or error signal to select the most suitable of the various phase on energization modes to obtain the desired motor performance.
Another object of the present invention is to provide gating means interposed between the two phase on, single phase on and various fractional phase on signal generating means and between the switching means, with the gating means having inputs responsive to signals from the signal selecting means to selectively gate the desired phase on mode logic signals from the signal generating means to the switching means for energization of the field windings in the desired phase on mode.
Yet another object of the present invention is to generate two phase on, single phase on and a plurality of fractional phase on modes with standard and inexpensive logic flip flops and NAND gates.
A further object of the present invention is to provide methods of controlling a multi-phase motor in a variety of winding energization modes by generating a plurality of logic signals representing the various energization modes and selecting the desired energization mode in response to a feedback signal derived from detection of rotor movement in response to energization of the windings.